1. Field of the Invention
The present invention relates to systems for reducion of radial vibrations of a rotating shaft.
2. Description of the Related Art
The invention concerns a system for active reduction of radial vibrations of a rotating shaft.
In piston engines, a multitude of various vibrations occurs as a result of the masses moving back and forth, as well as of the discontinuous combustion in the chamber. Besides vibrations of the overall engine, the drive shaft (i.e., the crankshaft) is excited in radial vibrations relative to the engine housing containing it. Because of the practically no-play mounting of the crankshaft in the radial direction, these vibrations are bending vibrations. Excitation of the vibrations occurs primarily through the radial components of the mass forces on the crank pins.
The bending vibrations represent a high stress on the crankshaft. Therefore, the crankshaft must be correspondingly heavily dimensioned in terms of strength. This requires, in particular, high-quality material and a costly production process (e.g., die forging). Furthermore, heavily loaded engines (such as diesel motors) must generally have a bearing after each crank throw. This produces great static overdetermination.
Resonance rises can occur in engines, especially those with a low number of cylinders, since the crankshaft along with the generally required flywheel forms an oscillatory system of low eigenfrequency, lying in the operating range of the internal combustion engine. This may produce resonance rises which can lead to fracture of the crankshaft.
To avoid resonance rises, vibration absorbers and dampeners are traditionally employed. A vibration absorber is an extra passive mass elastically coupled to the vibration system. The elastic coupling of the additional mass results in shifting of the original resonance frequency of the vibration system (more accurately, the original resonance frequency splits up into two different resonance frequencies). Through appropriate design of the extra mass and the stiffness of the elastic coupling, in many cases it is possible to make the new resonance frequencies no longer lie in the operating range, or at least no longer lie in an especially critical part of the operating range. Furthermore, by choosing a strongly dampening elastic coupling one can remove vibratory energy from the vibration system (by dissipation into heat) and reduce the size of any residual resonance rise (vibration dampener). In general, with the help of vibration absorbers/dampeners, one can master the problem of radial vibration in crankshafts.